Mammalian virus systems have been studied by combined electron microscopic and biochemical methods. Oligonucleotides and ribosome binding sites of the poliovirus genome have been mapped. Polio RNA fragments have been translated in vitro, and cloned in plasmids. Adenovirus early proteins have been localized in the cellular ultrastructure. Newly devised computer programs have been used to analyze nucleics for homologies, secondary structures, splice sites, promoter sites and recombination sites.